1. Field of the Invention
The present invention relates to a thermal module,.more specifically, a thermal module that uses a phase change material to temporarily store excess heat.
2. Description of the Prior Art
Quantities of heat generated by modern electrical components are often large enough to severely damage or destroy the components that generate the heat if proper precautions are not taken. These precautionary measures range from passive heat sinks to liquid refrigeration systems, but all have one common purpose, to transfer heat away from the generating device.
A well-known approach is to enlist the aid of a heat pipe. The conventional heat pipe is a hollow, partially evacuated tube. Inside the tube is a wick-like structure composed of a copper mesh or a similarly functioning component saturated with a predetermined fluid. When an end of the heat pipe is exposed to a heat source, the contained fluid at that end of the heat pipe boils, rapidly transferring heat to a cooler end of the heat pipe where the gas condenses. The condensed gas is sucked back to the region of highest heat through a capillary action of the wicks. This process effectively transfers heat many times quicker and farther than could be done by using a solid bar of a high heat conducting substance such as copper.
Many variations of heat pipes, including looped heat pipes, are used in varying situations with varying degrees of success. One of the most common uses of a heat pipe is to rapidly transfer heat from an electrical component to a heat dissipater, often a fanned or passive heat dissipater similar to a finned heat sink. Efficiency of such a system dictates that the heat dissipater must be able to dispose of unwanted heat about as rapidly as it is absorbed by the heat pipe, otherwise the related temperatures will continue to climb. In a prior art thermal module, this ability to dissipate heat as quickly as heat is absorbed is critical. If the temperature inside the condensing portion of the heat pipe exceeds the boiling point of the internal fluid, even temporarily, the heat pipe fails to function as intended and damage to related electrical components is a likely result.
Please refer to FIG. 1 of a graph of the levels of heat generated by the electrical components in a PC during a hypothetical period of use. Two horizontal divisions are shown. Amounts of heat below the passive cooling limit will not vaporize the fluid in the heat pipe and are dissipated passively. During time periods when the quantity of heat generated exceeds the passive cooling level, the fluid in the heat pipe boils and the heat pipe begins to actively transfer heat away from the electrical components and to the heat dissipater. It is obvious that usages such as those requiring frequent hard drive activity or CD access generate-more heat than typing in a word processing program. Therefore, the graph shows a typical series of peaks and valleys representing periods of higher and lower demands being placed on the system, and therefore higher and lower quantities of heat being generated.
However, because the efficiency of the system dictates that the heat dissipater must be able to dispose of unwanted heat about as rapidly as it is absorbed by the heat pipe, the entire thermal module must be designed around a thermal ceiling, the maximum quantity of heat that can be produced without damaging the electrical components. This thermal ceiling characteristic of the prior art thermal module makes it difficult to reduce the size of a thermal module, including the heat dissipater, a relatively large component occupying much needed space in many smaller applications. In fact, because faster CPUs generally generate larger amounts of heat, manufacturers face a serious conflict between the demand for a smaller product and the need to provide a large enough heat dissipater to accommodate the thermal ceilings in today""s PCs.
It is therefore a primary objective of the claimed invention to disclose a thermal module whose design is not dictated by a thermal ceiling, allowing the use of a smaller heat dissipater, while providing adequate thermal protection to the related electrical components.
The claimed invention includes a heat pipe for rapidly transferring heat from a heat absorber to a heat dissipater, and a heat storage also in flush contact with the heat pipe. The heat storage includes a phase change material (PCM) that changes from a solid state to a liquid state at a predetermined and specific temperature approximately corresponding to a reasonable thermal target. A flexible, thermally and electrically insulated casing inclosing the PCM allows it to be placed in small areas between the electrical components, occupying no more than what is normally wasted space.
It is an advantage of the claimed invention that the use of the phase change material, to temporarily store excess heat in a system, allows a smaller thermal module designed around a reasonable thermal target to provide adequate thermal protection.